As an alternative to canning or bottling food products, processed food products may be packaged within a sealed flexible container or pouch and then arranged on racks within a retort where the sealed pouches are subjected to high temperatures to sterilize and/or cook the food product. It is generally necessary to operate the retort at pressures above that of saturated steam at the process temperature in order to generally equalize the pressure of the atmosphere outside the pouches and the pressure within the pouches that develops due to heating of the gases trapped within the pouches and volatilization of water etc. from the product. Equalization of the pressure within and without the pouches reduces stress to the pouches minimizing seam failures that result in product destruction. Pressure equilization is normally accomplished by processing the container submerged in water with overriding air pressure.
More recently, advantages have been appreciated for retorting with a mixture of steam and air, the air being necessary to raise the pressure to above that of saturated steam at the processing temperature. Additional pressure through addition of pressurizing air is achieved at the expense of heat capacity relative to a pure steam atmosphere; however, the reduction of heat capacity can be compensated by increasing the flow rates of steam and air into the retort to achieve adequate heat transfer to the pouches.
It is highly desirable in a retort food processing system that heat transfer to the product within the pouches be uniform at all portions of the retort in order to assure complete cooking and sterilization of the product in all pouches without over heating product within other pouches. Heat transfer is a function of flow rate around a product as well as the temperature of the surrounding environment, and thus, thermal sensors which instantaneously record temperture changes are in themselves insufficient for measuring uniformity of heat transfer. In setting up and periodically checking retort food processing system, it would be desirable to provide apparatus that would simulate a pouch-packaged food product and measure heat transfer thereto. Such apparatus would be useful for measuring heat transfer uniformity in food processing in either a steam-air or a water type retort system where heat transfer in different regions is subject to localized flow conditions.
Several thermal simulators have been developed for measuring heat transferred into food products; however, none of the previously reported designs are truly adaptable or practical for simulating heat transfer into a flexible pouch in a retort for the purpose of measuring heat transfer at various regions. U.S. Pat. No. 3,964,313 describes a thermal simulator in the form of an outer can containing an open celled polymeric matrix uniformly distributing throughout the can a liquid having a pre-determined specific gravity. A thermal probe extending to the approximate center of the can is received through a threaded opening at one end of the can. This simulator is used to measure simulated heat transfer into a canned ham or the like.
The simulator described in the U.S. Pat. No. 3,984,313 patent is relatively expensive to produce comprising a number of components. It is also generally unadaptable to simulating heat transfer to a flexible pouch. A flexible pouch normally is quite thin compared to a can for cooking a canned ham, and very little tolerance in centering a thermal probe in a pouch simulator is permissable, whereas slight miscentering of a thermal probe within a larger container has a negligible effect. Substantial difficulties are encountered in precisely centering a thermocouple that is supported from a side of a thin metal can, and if a can type simulator were used, the thermal probe could extend into the can off-center a substantial percentage of the short distance between the opposed sides of a pouch-size container making it impossible to obtain the required uniformity between one simulator and another.
U.S. Pat. No. 4,340,610 describes a thermocouple locator for holding a thermocouple centered inside a flexible pouch that contains a food product to be processed. Although this arrangement is useful for directly measuring the temperature of an actual food sample, the arrangement has substantial disadvantages for measuring heat distribution within a retort. The arrangement is cumbersome and expensive to produce. Furthermore, the outer covering is an actual pouch, and although an actual flexible pouch simulates the actual cooking environment of food, the heat diffusivity to the centered thermocouple will depend on how the flexible pouch folds, bulges, etc., in response to heat, pressure and flowing gases. A container maintaining a uniform distance between the sides and the thermal probe will much more accurately measure the heat exchange provided at different locations within a retort.
Further examples of thermal measuring devices which measure the temperature of food, either directly or through simulation, are found in U.S. Pat. Nos. 1,729,298, 3,690,175, 3,754,465 and 3,812,716.
It is an object of the present invention to provide a device which simulates a food-containing retort pouch both in configuration and in heat diffusivity. It is also an object of this invention to use such a simulator to adjust conditions in a food processing retort.